Touch detection for a digitizer

ABSTRACT

A detector for providing position detection of objects over a sensor with a first and second set of conductor lines forming a grid with a plurality of junctions there between at which the conductor lines do not contact, includes a signal generator providing a signal to at least one conductor line of the first set of conductor lines, and circuitry detecting output arising from one or both of an electromagnetic stylus and one or more fingers when present. The output arising from each of the one or more fingers is detected from at least one conductor line of the second set of conductor lines in response to the signal provided to the at least one conductor line of the first set of conductor lines. The circuitry detects positions of one or both the electromagnetic stylus and each of the one or more fingers when present responsive to the output detected.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/153,343 filed on May 16, 2008, which is a continuation of U.S. patentapplication Ser. No. 11/727,301 filed on Mar. 26, 2007, now U.S. Pat.No. 7,843,439, which is a divisional of U.S. patent application Ser. No.10/757,489 filed on Jan. 15, 2004, now U.S. Pat. No. 7,372,455, whichclaims the benefit of priority of U.S. Provisional Patent ApplicationNos. 60/446,808 filed on Feb. 10, 2003, and 60/501,484 filed on Sep. 5,2003. The contents of all of the above applications are incorporated byreference as if fully set forth herein.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to a combined touch and stylus digitizerand, more particularly, but not exclusively to adaptations for thedetection of finger touch.

The popularity of computers has given rise to extensive research anddevelopment in the field of digitizers and touch screens. There are manyinventions describing touch panels but very few describe a digitizercapable of detecting both an EM stylus and finger touch using the samesensing device. U.S. patent application Ser. No. 09/629,334 “PhysicalObject Location Apparatus and Method and a Platform using the same”filed Jul. 7, 2000 assigned to N-trig Ltd and U.S. patent applicationSer. No. 09/628,334 “Transparent Digitizer” filed Aug. 28, 2003 alsoassigned to N-trig Ltd describe positioning devices capable of detectingmultiple physical objects, preferably styluses, located on a flat screendisplay.

U.S. patent application Ser. No. 10/270,373 “Dual Function Input DeviceAnd Method” filed Oct. 15, 2002 and assigned to N-trig Ltd, describes asystem capable of detecting electro magnetic objects and finger touchusing the same transparent sensor. In the disclosure, the finger touchdetection is implemented by a matrix of resistive stripes that aremerged into the EM detection pattern. A special separation layer isplaced between the conductor layers so as simultaneously to enable touchstripe contact and prevent contact between the EM lines. Additionalelectronics are required to drive and read the touch signals from thesensor. The major disadvantage of this method is the additionalcomplexity to both sensor and electronics.

U.S. Pat. No. 3,944,740 employs an input pad mounted over the top of aplasma panel display. The input pad is a matrix of conductive rows andcolumns that are arranged so that a stylus having a conductive tip canshort circuit a row electrode and a column electrode at its point ofcontact, with current conducted through the row and column electrodesrepresenting the stylus location. U.S. Pat. No. 4,639,720 employs asimilar idea using conductive pixels rather then a matrix of rows andcolumns.

Two major disadvantages of the above patents are low resolution of thestylus detection and inability to specifically detect an electromagnetictype stylus. Since the stylus is detected only when it shortcuts twoadjutant lines\pixels it is impossible to track it when it is locatedbetween the lines\pixels. Therefore the resolution of the stylusdetection is limited to the proximity of the lines\pixels. The stylusdetection, as disclosed in these patents, is inherently different fromthe one described in the presently preferred embodiments. U.S. Pat. No.6,239,389 describes a method of finger detection by measuring a firstset of voltage values from each conductive line, and calculating aweighted average of these samples with respect to samples made withoutthe presence of a finger. The sensor is constructed from a series ofplates arranged in rows and columns and connected by a conductive line.The main disadvantages of this method are that it requires an arithmeticunit for calculating the weighted average of the sampled values, it doesnot allow the detection of an EM stylus and the sensor is nottransparent.

U.S. Pat. No. 4,550,221 describes a sensor array comprising of series ofconductive plates/pixels connected by a conductive wire. A finger touchchanges the pixel's capacitance with respect to ambient ground. Thechange is detected and translated to indicate a finger's position. Thedisclosure does not allow the detection of an EM stylus together withfinger detection. The sensor's plates\pixels are not transparent andtherefore cannot be mounted on a display screen.

U.S. Pat. No. 4,293,734 employs two current sources drivingpredetermined currents through each end of the antenna. The finger'sposition is calculated using Kirchoff's laws for current leakage throughthe finger to the ground. Disadvantages of the detection systemdisclosed therein are that it does not allow the detection of an EMstylus. Rather it requires current flows from both ends of theconductive surface which is in evidently power consuming. Furthermore,the detection is analog and involves relatively complicated circuitry.

U.S. Pat. No. 6,452,514 employs two or more electrodes arranged tocreate an electric field transmitted through an adjacent dielectric,which can be disturbed by the proximity of a conductive object. A chargetransfer measurement circuit is connected to one of the electrodes todetermine the existence of the object. The disclosure teaches connectingeach electrode to an individual charge transfer measurement unit.Disadvantages of the above invention are the inability to detect an EMstylus, low update rate and limited resolution.

U.S. Pat. No. 6,583,676 describes a method of detecting a finger's addedcapacitance upon application of a frequency change. A calibrationcircuit and method for a proximity/touch detector allow automaticcalibration to the proximity/touch detector components, chassis affects,and ambient conditions such that initial factory calibration andperiodic manual calibration are not needed. The calibration circuitswitches a capacitance into the input capacitance of a Schmitt triggerfree running oscillator to change the output frequency of theoscillator. A capacitive sensor forms part of the input capacitance. Thechange in frequency simulates the frequency shift associated with thedifference in input capacitance generated when an object, such as afinger, is touching the capacitive sensor and when the capacitive sensoris free from contact with the object. The most evident disadvantages ofthis invention is the need for additional hardware and the inability todetect an EM stylus.

Other methods of finger detection can be founds in U.S. Pat. Nos.6,587,093, 6,633,280, 6,473,069, and 6,278,443. The above describemethods of finger detection all inherently different from the methodsdescribed hereinbelow, and none combine the ability to sense both an EMstylus and a finger touch.

There is thus a widely recognized need for, and it would be highlyadvantageous to have, a digitizer system devoid of the abovelimitations.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided adetector for providing position detection of a first kind together withposition detection of a second kind, the detector comprising:

a sensor,

a patterned arrangement of sensing conductors extending within thesensor, and

detection circuitry associated with the arrangement for detectingsignals at same sensing conductors arising from the position detectionof a first kind and signals arising from the position detection of asecond kind, therefrom to detect positions at the sensor.

Preferably, the position detection of a first kind comprisesresonance-based object detection of an object able to produce anelectromagnetic resonant field.

Preferably, the position detection of a first kind comprisescapacitive-based touch detection.

Preferably, the position detection of a first kind comprisesresonance-based object detection of an object able to produce anelectromagnetic resonant field and the position detection of a secondkind comprises capacitive-based touch detection.

Preferably, the detection circuitry is capable of detecting interactionsof the first kind and the interactions of the second kindsimultaneously.

Preferably, the detection circuitry is capable of detecting interactionsof the first kind and the interactions of the second kind independently.

Preferably, the sensor is located over a detection region, and comprisesan oscillator for providing an oscillating signal, excitation circuitryfor providing an excitation signal capable of exciting a resonantcircuit of an electromagnetic stylus-type object, wherein the patternedarrangement comprises conductive elements extending over the detectionregion, and wherein the detection circuitry is adapted for detecting thecapacitive effect of a conductive object, such as finger touch, andresonance from the electromagnetic stylus-type object at the at leastone conductive element.

Preferably, the oscillator is connected to provide the oscillatingsignal to the excitation circuitry and also to provide an excitationsignal for the capacitive based touch detection.

Preferably, the sensor is substantially transparent and suitable forlocation over a display screen.

Preferably, the detection region is the surface of a display screen andwherein the sensor including the at least one conductive element issubstantially transparent.

The detector may comprise a plurality of conductive elements and thedetection circuitry may comprise a differential detector arrangementassociated with the sensing conductors for detecting differences betweenoutputs of the conductors.

Preferably, the sensing circuitry is configured for sensing a signal atthe at least one sensing conductive element induced by a touch of aconductive object subjected to a transmission of the oscillated signal.

Preferably, there is provided at least a second conductive elementlocated within the sensor and having a junction with the one conductiveelement, wherein the oscillator is applied to one of the conductiveelement and the junction is configured such that a touch by a capacitivebody part causes an a.c short at the junction, the detector beingconfigured to detect a resulting oscillating signal at the secondconductive element and therefrom to infer the touch.

Preferably, the detection circuitry is adapted to detect a signal at theat least second conductive element for interpretation as a number oftouching objects.

Preferably, multiple resonance-based objects can be detected based onthe interpretation of properties of the detected signal.

Preferably, multiple conductive objects can be detected based on theinterpretation of properties of the detected signal.

Preferably, the oscillator is connected to oscillate at least one of thedetector, part of the detector and the at least one conductive elementwith respect to a reference voltage level, thereby to permit acapacitive current flow between a conductive touching object and the atleast one conductor.

Preferably, the sensor is configured with a transparent medium betweenitself and an underlying display screen.

Preferably, the transparent medium comprises an air gap.

According to a second aspect of the present invention there is provideda detector for detecting touches by conductive objects making capacitivecontact with a transparent sensor located over a display screen, thedetector comprising:

a patterned arrangement of sensing conductors extending into the sensor,

a source of oscillating electrical energy at a predetermined frequency,and

detection circuitry for detecting a capacitive influence on the at leastone sensing conductor when the oscillating electrical energy is applied.

Preferably, the detection circuitry comprises a differential detectorarrangement associated with the sensing conductors for detectingdifferences between outputs of the conductors.

Preferably, the source of oscillating electrical energy is configured totransmit the energy into the conductive object, and the sensingcircuitry is configured for sensing a signal at the at least one sensingconductive element induced by a touch of a conductive object subjectedto the transmitted oscillated signal.

The detector is preferably configured to interpret a property of asignal detected at the at least one conductor in terms of a number oftouching conductive objects.

Preferably, there is provided at least a second conductor located withinthe sensor and having a junction with the at least one conductor,wherein the source of oscillating electrical energy is applied to one ofthe conductors and the junction is configured such that a touch by aconductive object causes an a.c short at the junction, the detectorbeing configured to detect the oscillating signal at the secondconductor as the capacitive effect and to infer the touch.

Preferably, the detection circuitry is configured to interpret aproperty of a detected signal as a number of touches of a correspondingconductor.

The detector may comprise a matrix of first sensors aligned in a firstdirection and second sensors aligned in a second direction with aplurality of junctions in between. There may additionally be provided atabulation of leakage capacitance values for each junction, the detectorbeing configured to use the leakage capacitance values to correctreadings at each conductor.

Preferably, the source of oscillating electrical energy is connected tooscillate at least one of the detector, part of the detector and the atleast one conductor with respect to a reference voltage level, therebyto permit a capacitive current flow between the conductive object andthe at least one conductor.

Preferably, the source of oscillating energy is connected to oscillate afirst part of the detector, and wherein the first part is connected to asecond part not subject to oscillations via a communication connectionunaffected by the potential difference between the first and the secondparts of the detector.

Preferably, the communication connection comprises at least onedifferential amplifier.

Preferably, the sensor is configured with a transparent medium betweenitself and the display screen.

Preferably, the transparent medium comprises an air gap.

Preferably, the sensor comprises a grid of conductors arranged within alayer thereof.

Preferably, the conductors are connected pairwise to amplifiers.

Preferably, the amplifiers are differential amplifiers each having apositive input and a negative input and wherein one conductor of thepair is connected to the positive input and a second conductor of thepair is connected to the negative input.

The detector may comprise a compensation table for providing acompensation value at each conductor to compensate for static noise.

The detector may be configured to update the compensation table uponsystem startup.

The detector may be configured to use an ambiguous object detection as atrigger to refresh the compensation table.

Preferably, any combination of number, phase and position data fromdetected signals are used to define ambiguity in object detection.

According to a third aspect of the present invention there is provided amethod of touch sensing at a matrix of sensing conductors located in atransparent sensor over an electronic display screen, comprising:

providing an oscillating signal at a predetermined frequency, and

measuring the conductors for capacitive effects on the conductors due totouch thereon.

The method may comprise providing the oscillating signal to an externaltransmitter to energize a touching body part.

Preferably, the matrix comprises first conductors aligned in a firstdirection and second conductors aligned in a second direction, themethod comprising providing the oscillating signal to the firstconductors and sensing the oscillating signal at any of the secondconductors to which the signal has been passed by a capacitive linkcaused by a touching conductive object.

The method may comprise providing the oscillating signal to at least theconductors such that a conductive touching body drains current from arespective conductor.

The method may comprise using the oscillating signal to oscillate adetection mechanism comprising the conductors wherein the oscillateddetection mechanism is simultaneously isolated from common ground.

The method may comprise using the oscillating signal to oscillate afirst part of a detection mechanism, the first part comprising theconductors,

isolating the first part from a second part, and

using the isolated second part to communicate touch detection outputs toexternal devices.

According to a fourth aspect of the present invention there is provideda method of manufacture of a touch detector for an electronic displayscreen, comprising:

providing an oscillation signal source,

embedding a grid of transparent conductors within at least onetransparent foil,

placing the transparent foil over the electronic display screen, and

providing detection circuitry for detecting capacitive effects on theconductors.

The method may comprise applying an excitation unit about the electronicscreen for exciting an electromagnetic stylus, so that location of thestylus is detectable at the grid of transparent conductors.

According to a fifth aspect of the present invention there is provided aTouch detection apparatus comprising:

a sensor comprising at least one sensing conductive element,

an oscillator for providing an oscillation signal,

a transmitter, associated with the oscillator, for transmitting theoscillation signal in the vicinity of the sensor,

sensing circuitry for sensing a signal at the at least one sensingconductive element induced by a touch of a conductive object subjectedto the transmitted oscillated signal.

According to a sixth aspect of the present invention there is provided atouch detection apparatus comprising:

a sensor comprising a grid array of conductors in a first sense andconductors in a second sense and having junctions therebetween,

an oscillator for providing an oscillation signal to conductors in thefirst sense,

detection circuitry for detecting the oscillation signal whentransferred via the junctions to conductors in the second sense, thetransference being indicative of capacitive coupling induced by a touchof a conductive object touching the sensor at a respective junction.

According to a seventh aspect of the present invention there is providedtouch detection apparatus comprising:

a sensor comprising at least one sensing conductive element,

an oscillator for providing an oscillation signal, the oscillationsignal being applied to at least part of the apparatus including the atleast one sensing conductive element, and

detection circuitry for detecting a.c. grounding of the at least onesensing conductive element due to a capacitive connection to aconductive object touching the sensor.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. The materials, methods, andexamples provided herein are illustrative only and not intended to belimiting.

Implementation of the method and system of the present inventioninvolves performing or completing certain selected tasks or stepsmanually, automatically, or a combination thereof. Moreover, accordingto actual instrumentation and equipment of preferred embodiments of themethod and system of the present invention, several selected steps couldbe implemented by hardware or by software on any operating system of anyfirmware or a combination thereof. For example, as hardware, selectedsteps of the invention could be implemented as a chip or a circuit. Assoftware, selected steps of the invention could be implemented as aplurality of software instructions being executed by a computer usingany suitable operating system. In any case, selected steps of the methodand system of the invention could be described as being performed by adata processor, such as a computing platform for executing a pluralityof instructions.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings. With specific reference now tothe drawings in detail, it is stressed that the particulars shown are byway of example and for purposes of illustrative discussion of thepreferred embodiments of the present invention only, and are presentedin the cause of providing what is believed to be the most useful andreadily understood description of the principles and conceptual aspectsof the invention. In this regard, no attempt is made to show structuraldetails of the invention in more detail than is necessary for afundamental understanding of the invention, the description taken withthe drawings making apparent to those skilled in the art how the severalforms of the invention may be embodied in practice.

In the drawings:

FIG. 1A is a simplified block diagram showing a generalized embodimentof the present invention;

FIG. 1B is a simplified diagram illustrating an embodiment of thepresent invention in which oscillating energy is transmitted to afinger;

FIG. 2 is a simplified diagram illustrating an embodiment of the presentinvention in which the touching finger provides a capacitive linkbetween sensing conductors on a grid;

FIG. 3 is a circuit diagram illustrating the electrical theory of theembodiment of FIG. 2;

FIG. 4 is a simplified schematic diagram illustrating an embodiment ofthe present invention in which the detection device is floated using asignal that oscillates with respect to a reference signal and wherein afinger incident upon a conductor provides a capacitive path to ground;

FIG. 5 is a circuit diagram illustrating one version of the embodimentof FIG. 4;

FIG. 6 is a circuit diagram illustrating a variation of the embodimentof FIG. 4;

FIG. 7 is a circuit diagram illustrating another variation of theembodiment of FIG. 4, in which the conductors are oscillated directly;

FIG. 8 is a circuit diagram illustrating a variation of the embodimentof FIG. 7 in which the conductors are oscillated from their far ends;

FIG. 9 is a block diagram of a variation of the embodiment of FIG. 4 inwhich isolation is provided by a DC to DC converter;

FIG. 10A is a block diagram illustrating another variation of theembodiment of FIG. 4 in which isolation by a DC to DC converter isprovided between two parts of the detector;

FIG. 10B is a block diagram illustrating a modification to theembodiment of FIG. 10A to permit communication between the two parts ofthe detector;

FIG. 11 is a block diagram illustrating coil-based isolation of thedetector according to an embodiment of the present invention;

FIG. 12 is a block diagram illustrating a variation of the embodiment ofFIG. 11 in which the coil based isolation is used for a part of thedetector;

FIG. 13 is a block diagram illustrating floating of the detector byplacing tandem oscillators on the positive and ground power supplyrails;

FIG. 14 is a simplified block diagram illustrating how the sameexcitation circuitry can be used for stylus and finger touch sensingaccording to a preferred embodiment of the present invention;

FIG. 15 is a theoretical circuit diagram illustrating sources of steadystate noise that affect touch measurements in the present embodiments;

FIGS. 16A and 16B illustrate a grid of conductors and tabulation, bothof magnitude and phase, of noise effects for the respective conductors;

FIG. 17 is a block diagram of touch detection apparatus able to use thetabulation of FIG. 16B in order to correct touch readings;

FIG. 18 is a simplified diagram illustrating signal patterns indicativeof finger touches;

FIG. 19 is a simplified flow chart illustrating touch measuringprocedures according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present embodiments comprise a digitizer that allows finger clicksand movement detection on flat panel displays, in such a way that thesame sensing infrastructure can be used for electromagnetic (EM) stylusdetection. The digitizer is designed to work in conjunction with apatterned transparent conductive foil system, which allows for detectingthe location of an electro magnetic stylus on top of an electronicdisplay surface. Some of the presently preferred embodiments use fingerinduced capacitance connecting the sensor lines as a method of fingerdetection. The present embodiments include inter alia a method ofidentifying the presence and location of the finger by measuring thedifferential signal between two different sensor antennas. In thepreferred embodiments the currents are driven from one end of theantenna, and the information is then sensed and digitized using thedetector as will be described in greater detail hereinbelow.

Whilst the prior art teaches connection of a separate charge sensor orthe like to each electrode, the present embodiments are able to utilizethe differential signal generated between two electrodes.

One of the methods disclosed hereinbelow involves measuring voltagedifferences due to the finger's adding a capacitive short circuit to theground.

The primary use of the preferred embodiments is to allow a natural andintuitive operation of an “on-screen-keyboard”, in devices such as thetablet PC, separately, in addition and in parallel to the operation ofan accurate electro magnetic stylus.

In the following description there are presented three methods ofimplementing touch sensors using the same detector unit and sensor gridused for the detection of an EM stylus. The sensing methods disclosedmay require adjustments for given circumstances and devices, as will beapparent to the person skilled in the art. However, all methods aredesigned to enable the simultaneous and independent detection of an EMstylus in a manner similar to that disclosed in U.S. patent applicationSer. No. 10/649,708 to the present assignee, filed 28 Aug. 2003, andclaiming priority from U.S. Provisional Patent Application No.60/406,662. Detection of finger touch and EM stylus is independent andcan be performed simultaneously or at different times. It is left to thediscretion of the user whether to use the presently disclosedembodiments in order to implement a detector for one kind of interactionalone (i.e. finger touch or EM stylus) or to allow the detection of bothkinds of interactions.

In the preferred embodiments of the present invention, the same detectorcan detect and process signals from an Electro Magnetic Stylus whetherit is placed in contact with, or at a short distance from, the surfaceof a flat panel display. For example detection may be carried out in themanner described in U.S. patent application Ser. No. 09/628,334“Physical Object Location Apparatus and Method and a Platform using thesame” assigned to N-trig Ltd, and U.S. patent application Ser. No.09/628,334 “Transparent Digitizer” again assigned to N-trig Ltd). At thesame time the detector can be used to detect a user's finger placed onthe same display, as will be described hereinbelow. In other embodimentsof the present invention the finger detection may function solely, or incombination with any other input device.

The principles and operation of a digitizer according to the presentinvention may be better understood with reference to the drawings andaccompanying description.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not limited in its applicationto the details of construction and the arrangement of the components setforth in the following description or illustrated in the drawings. Theinvention is capable of other embodiments or of being practiced orcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and should not be regarded as limiting.

Reference is now made to FIG. 1A, which is a schematic diagramillustrating a generalized embodiment of the present invention. In FIG.1A a sensor 2 comprises at least one electrical conductor 4. In thetypical case there is more than one conductor, and the conductors areset in an arrangement or pattern over the sensor, most often as a gridwhich extends over a surface such as an electronic screen for whichtouch sensing is required. A detector 6 picks up the output from theconductors. An oscillator 8 provides oscillations or a.c. energy to thesystem comprising the sensor and detector. In one embodiment, the systemis not initially a.c. coupled. However a conductive object, includingbody parts such as fingers are capacitive and therefore touch by afinger or the like completes the a.c. coupling within the system andallows the touch to be sensed. Alternatively a touch by the finger mayprovide an a.c. short circuit to ground for a given conductor, againallowing the touch to be sensed.

A preferred embodiment detects touch as described above and additionallyallows the location and identification of physical objects, such asstyluses. The location of the physical objects is sensed by an electromagnetic transparent digitizer, preferably constructed on top of adisplay, and it is a feature of some of the preferred embodiments thatthe electromagnetic transparent digitizer makes use of the samecomponents as the touch digitizer described herein, so that the twotypes of detection can be incorporated into a single digitizer, as willbe explained hereinbelow. The construction of a suitable electromagnetictransparent digitizer is described in U.S. patent application Ser. No.09/628,334. This application describes a sensing device that is capableof detecting multiple physical objects located on top of a flat screendisplay.

The various components and functionality manner of the transparentdigitizer are as follows.

1.

a. Sensor

As described in the above referred to applications and used in thepresently preferred embodiments, the sensor comprises two transparentfoils, one containing a set of vertical conductors and the other a setof horizontal conductors. The grid of conductive lines is made ofconductive materials patterned on the transparent foils, which may forexample be PET foils. In different embodiments, the present inventionsensor could be implemented on other transparent conductive materialssuch as ITO. In a preferred embodiment, the resistance of the conductivelines is relatively high and it might exceed 100 KOhms for a line.Usually, higher resistance of transparent conductors results in a highertransparency of the material.

Further information regarding the construction of the sensor isavailable from U.S. provisional patent application 60/406,662(sub-chapter 4.2 entitled: “Sensor”) and corresponding U.S. patentapplication Ser. No. 10/649,708 filed Aug. 28, 2003, both assigned toN-Trig. Ltd. the contents of both of which are hereby incorporated byreference.

b. Front End Unit

As described in the above referred to applications and used in thepresently preferred embodiments, the detectors include front end units,which are the first stage where sensor signals are processed.

Front end units function as follows:

Differential amplifiers amplify the signals and forward the result to aswitch. The switch selects the forwarded inputs that appear to needfurther processing. In other words the switch filters out those inputswhere no activity appears to be occurring. The selected signals areamplified and filtered by a Filter & Amplifier arrangement prior tosampling. The output of the filter and amplifier arrangement is thensampled by an A to D converter and sent to a digital unit via a serialbuffer.

For further information see U.S. provisional patent application60/406,662 (sub-chapter 4.3 entitled: “Front end”) and correspondingU.S. patent application Ser. No. 10/649,708 filed Aug. 28, 2003, bothassigned to N-Trig. Ltd. the contents of both of which are herebyincorporated by reference.

c. Digital Unit

As described in the above referred to applications and used in thepresently preferred embodiments, there is provided a digital unit ormicroprocessor, which functions as follows:

A front-end interface receives serial inputs of sampled signals from thevarious front-end units and packs them into parallel representation.

In one embodiment, all of the sensor inputs lines are sampled at thesame time during one system cycle.

A digital signal processor (DSP) core, which performs the digital unitprocessing, reads the sampled data, processes it and determines theposition of the physical objects, such as stylus or finger.

A calculated position is sent to the host computer via link.

For further information see U.S. provisional patent application60/406,662 (sub-chapter 4.4 entitled: “Digital unit”) and correspondingU.S. patent application Ser. No. 10/649,708 filed Aug. 28, 2003, bothassigned to N-Trig. Ltd. the contents of both of which are herebyincorporated by reference. The above-mentioned applications discusssignal processing and position determination for signals emanating froman electromagnetic EM stylus, but do not provide any disclosureregarding finger detection. As will be explained below, in the presentembodiments, finger touch may be detected using compatible signals onthe same detection conductors which are processed in substantially thesame way. It makes no substantial difference to the DSP core or to theintervening electronics whether the signals originate from a finger orfrom a stylus.

d. Detector

A detector consists of the digital unit and the Front end units, asdescribed above.

2. Stylus Detection

As described in the above referred to applications and used in thepresently preferred embodiments, simultaneous and separate inputs,either from a stylus or from a finger, can be detected.

The preferred embodiment of the present invention utilizes a passive EMstylus that includes a resonance circuit. The resonance circuit isformed by an inductor and a capacitor which is excited to oscillate in abasic resonance frequency. In some exemplary embodiments, contactbetween the stylus tip to the surface closes a touch switch and connectsan additional capacitor to the resonant circuit in parallel to theexisting capacitor. This changes the effective capacity and thus changesthe resonance frequency. The digital unit detects the change infrequency and interprets the touch based on the detected change, e.g.left click, right click or both.

An external excitation coil that surrounds the sensor excites theresonance circuit within the stylus. The resonance circuit emitsradiation which can be detected by the conductors. The exact positionand unique identity of the stylus can then be determined by the detectoras a result of processing the signals sensed by the sensor.Alternatively, the stylus can be internally powered using a battery.

For further information see U.S. provisional patent application60/406,662 (sub-chapter 4.5 entitled: “Stylus”) and corresponding U.S.patent application Ser. No. 10/649,708 filed Aug. 28, 2003, bothassigned to N-Trig. Ltd. the contents of both of which are herebyincorporated by reference.

Algorithms

In the preferred embodiments of the present invention the basicdetection operation cycle consists of averaging, decay compensation,windowing, FFT/DFT, peak detection, interpolation, error compensation,filtering and smoothing. The cycle is substantially the same whether afinger touch or a stylus is being detected with the notable exceptionthat, as disclosed hereinbelow, the sources of noise and thus the typesof appropriate error compensation differ.

For further information see U.S. provisional patent application60/406,662 (sub-chapter 4.6 entitled: “Algorithms”) and correspondingU.S. patent application Ser. No. 10/649,708 filed Aug. 28, 2003, bothassigned to N-Trig. Ltd. the contents of both of which are herebyincorporated by reference.

3. Finger Detection

a. First Embodiment

This method utilizes an electromagnetic wave transmitted from either anexternal source or by the sensor components and received by the userbody. When the user's finger touches the sensor the EM energy transfersfrom the user to the sensor. The detector processes the signal anddetermines the finger's position.

Reference is now made to FIG. 1B, which is a general description of afirst finger detection apparatus according to the present invention. Anexternal source 10 transmits electro-magnetic wave energy, which isabsorbed by the user's body. If the user now touches the sensor 12 acapacitance is formed between the finger 14 and the sensor conductors.The received signal is at a frequency that allows it to pass through thecapacitance at the level typically formed, and thus the received signalpasses from the user's finger 14 to the sensor 12. Detector 16, whichprocesses the sensed signals, determines the position of the user'sfinger.

In a preferred embodiment, the external energy source is producedinternally by the system using a dedicated transmitter. In otherembodiments, the energy source could be a side effect of other parts ofthe system, such as transmission of a DC-to-DC converter, or even bebackground noise entirely unrelated to the system, such as electronicnetwork noise.

In a preferred embodiment, the same sensor conductors that are used forsensing the EM stylus also sense the signal transmitted by the user'sfinger. Furthermore, the analog processing of the signals and thesampling of the signals is similar to that of the EM stylus and isperformed by the same hardware, as explained elsewhere herein. In otherembodiments, it may be more convenient to use different conductors forsensing the fingers and the stylus respectively, and thus additionalelectronics is added, alongside the stylus sensing arrangement, forprocessing and sampling the finger signals.

In a preferred embodiment both EM stylus signals and user finger signalsare received and processed simultaneously so that both types of inputcan be detected at the same time. This is possible because, as explainedelsewhere herein, the types of input signals from the sensors areessentially the same. In other embodiments, the system can alternatebetween detection of fingers and stylus.

The sensor requires a reference voltage level and a convenient referenceis ground. In one embodiment of the present invention however, thesensor reference is dissociated with the electric network ground. Thereason is that, whilst ground is used, the electric potential of theuser body is close to the potential of the sensor reference and thesignal that is sensed as a result is low. As the reference is moved awayfrom ground the signal to be sensed is increased.

In other embodiments, especially if a dedicated transmitter is used, thesensor reference can nevertheless be connected to the ground of theelectric network. That is to say, the system as a whole can be operatedwhether it is connected to the ground or not. However, when the systemis connected to ground, it is preferable to use a dedicated transmitter.This is because, if a dedicated transmitter is not used on a groundedsystem then the signal resulting from a finger touch is weaker andtherefore harder to detect.

The finger touch position is determined by processing the relativemagnitude (and phase) of the signals that are detected on both axes, aswill be explained in greater detail below. Accurate positioning iscalculated by interpolation-type processing of the signals sensed byother conductors close to the point of finger touch.

In a preferred embodiment, the signals are transformed from the timedomain to the frequency domain. If the energy received by the user'sbody is concentrated at a specific frequency, processing is carried outon that specific frequency, and other frequencies are simply ignored.Otherwise, processing may be performed on a group of frequencies.

In a preferred embodiment, different conductors are sampled at differenttime slots. It is assumed that the size of the time slots is chosen tobe sufficiently small that the characteristics of the signal do notchange over a few time slots. However, should the signal neverthelesschange between successive measurements, such as when the finger receivesrandom noise, then, in this embodiment, the measurement procedurechanges and all conductive lines are sampled at the same time.

In a preferred embodiment, the energy transmission source is external tothe sensor. In other embodiments, the energy is transmitted by one ofthe sensor components, for example the sensor excitation coil, thesensor matrix or any other conductor that is added to the sensor inorder to specifically transmit the energy. In one embodiment it ispossible to transmit the energy by alternating between a firsttransmitter that is orthogonal to one set of sensing conductors and asecond transmitter that is orthogonal to the other set of conductors.Regarding the concept of a transmitter being orthogonal to a conductor,when transmitting from an antenna that is orthogonal to one conductoraxis and parallel to the other conductor axis—signals received on theconductors that are in parallel are very strong, hence a signal inducedby a finger is undetected. However, the conductors orthogonal to thetransmitting antenna are hardly disturbed by it. Hence, a signal inducedby a finger is detectable on the conductors that are orthogonal to thetransmitting antenna. Now in all the preferred embodiments,electromagnetic (EM) stylus excitation is performed prior to sampling,whereas finger detection energy is transmitted during sampling.Consequently it is possible to produce both stylus excitation and fingerexcitation, that is to say transmission, signals using the samehardware, typically a signal generator. The two signals are simplytransmitted by the same physical antennas at different time slots.Furthermore the stylus sampling procedure includes an excitation periodand a separate sampling period which is subsequent to the excitationperiod. Thus, whilst the stylus is being sampled the antenna can alreadystart to generate the signal for finger detection. Hence both objectscan be sensed in the finger excitation phase. Alternatively, a stylusexcitation signal generator may be provided as a separate unit from thefinger detection signal generator.

In a preferred application the detector is capable of detecting multiplefinger touches simultaneously. As long as different conductors sensedifferent fingers the detection of multiple fingers is similar todetection of a single finger. However, if more than one finger is sensedby the same antenna than a higher signal magnitude is sampled on therespective antenna. The detector is simply required to process themagnitudes of the signals to distinguish the multiple finger touches.

Drawbacks to the first embodiment are:

-   -   A dramatically reduced signal provided by the finger when the        power supply of the system is grounded. This disadvantage makes        a digitizer based thereon suitable mainly for devices powered by        battery or those powered by a source highly isolated from the        ground.    -   The need to transmit and therefore potentially interfere with        other equipment.    -   Dependency on the distance from the user to the transmitter;        meaning the further away the user is from the transmitter the        lower is the signal. The resulting variation can lead to        reliability problems.

b. Second Embodiment

The second embodiment does not require transmitting an EM signal to theuser's body. Rather, even without the influence of an EM signal, theuser's finger adds a capacitance that connects two orthogonal sensorlines.

Reference is now made to FIG. 2, which is a general description of thesecond finger detection embodiment of the present invention. Atwo-dimensional sensor matrix 20 lies in a transparent layer over anelectronic display device. An electric signal 22 is applied to a firstconductor line 24 in the two-dimensional sensor matrix 20. At eachjunction between two conductors a certain minimal amount of capacitanceexists. A finger 26 touches the sensor 20 at a certain position andincreases the capacitance between the first conductor line 24 and theorthogonal conductor line 28 which happens to be at or closest to thetouch position. As the signal is AC, the signal crosses by virtue of thecapacitance of the finger 26 from the first conductor line 24 to theorthogonal conductor 28, and an output signal 30 may be detected.

It will be appreciated that depending on the size of the finger and thefineness of the mesh of conductors, any number of the orthogonalconductors will receive some capacitive signal transfer, andinterpolation of the signal between the conductors can be used toincrease measurement accuracy.

It will also be appreciated that a capacitive coupling of this naturetypically introduces a phase shift in the signals. The significance ofthe phase shift will be discussed in greater detail below.

Reference is now made to FIG. 3, which is the theoretical electricequivalent of FIG. 2. Parts that are the same as in previous figures aregiven the same reference numerals and are not referred to again exceptas necessary for understanding the present embodiment. The transmittedsignal 22 is applied to the Horizontal conductor 24. The finger 26 thattouches the sensor creates two capacitors, C1 40 and C2 42 that transferthe signal from the horizontal line to the finger and from the finger tothe vertical conductor 28. An output signal 30 is detected on the edgeof the vertical conductor in the case of finger touch.

In a preferred embodiment, the two-dimensional matrix of conductors usedfor sensing the stylus is the same one used for sensing the fingers.Each conductive line is used for reception of both stylus signals andfinger signals. Each one of the lines can serve either for reception orfor injection of signals. The detector controls the switching of thesensor conductors between reception and transmission modes.

Each horizontal conductor overlaps with each vertical conductor, and theregions of overlap between horizontal and vertical conductors alsoresult in a certain amount of parasitic capacitance. Furthermore theindividual junctions may give rise to different levels of capacitance.The capacitance causes a small amount of signal transfer between theconductors even if no finger is present. In a preferred embodiment, thedetector actually learns the amount of parasitic current transfer foreach individual junction and subtracts this value from the sampledsignals.

The goal of the finger detection algorithm, in this method, is torecognize all of the sensor matrix junctions that transfer signals dueto external finger touch. It should be noted that this algorithm ispreferably able to detect more than one finger touch at the same time.

A number of procedures for detection are possible. The most simple anddirect approach is to provide a signal to each one of the matrix linesin one of the matrix axes, one line at a time, and to read the signal inturn at each one of the matrix lines on the orthogonal axis. The signal,in such a case, can be a simple cosine pattern at any frequency withinthe range of the sampling hardware and detection algorithms. If asignificant output signal is detected, it means that there is a fingertouching a junction. The junction that is being touched is the oneconnecting the conductor that is currently being energized with an inputsignal and the conductor at which the output signal is detected. Thedisadvantage of such a direct detection method is that it requires anorder of n*m steps, where n stands for the number of vertical lines andm for the number of horizontal lines. In fact, because it is typicallynecessary to repeat the procedure for the second axis so the number ofsteps is more typically 2*n*m steps. However, this method enables thedetection of multiple finger touches. When an output signal is detectedon more then one conductor that means more than one finger touch ispresent. The junctions that are being touched are the ones connectingthe conductor that is currently being energized and the conductors whichexhibit an output signal.

A faster approach is to apply the signal to a group of conductors on oneaxis. A group can comprise any subset including all of the conductors inthat axis, and look for a signal at each one of the conductors on theother axis. Subsequently, an input signal is applied to a group of lineson the second axis, and outputs are sought at each one of the conductorson the first axis. The method requires a maximum of n+m steps, and inthe case in which the groups are the entire axis then the number ofsteps is two. However, this method may lead to ambiguity on those rareoccasions when multiple touches occur simultaneously at specificcombinations of locations, and the larger the groups the greater is thescope for ambiguity.

An optimal approach is to combine the above methods, starting with thefaster method and switching to the direct approach upon detection of apossible ambiguity.

c. Third Embodiment

The third embodiment uses a potential difference between the user'sfinger and the system to determine the finger position.

Reference is now made to FIG. 4, which is a simplified schematic diagramillustrating the third preferred embodiment of the finger detection ofthe present invention. A detector 60 is connected to ground 62. Thedetector is connected to an oscillator 64 that provides an alternatingsignal which can cause the detector potential to oscillate with respectto ground potential. The oscillating potential is applied to sensor 66.

In operation the detector 62 oscillates in reference to the commonground potential. As a user's finger 68 touches the sensor 66, acapacitance is formed between the finger and the sensor conductors. Nowthe user's body potential does not oscillate in reference to earth whilethe sensor's potential does oscillate in reference to the common groundpotential. Thus an alternating difference in potential between thesensor and the user is formed. An alternating current therefore passesfrom the sensor through the finger to the ground. The current isinterpreted as a signal that passes from the user's finger 68 to thesensor 66. The detector 62 processes the sensed current and determinesthe location of the user's finger according to the magnitude, that isthe signal level, on certain sensor conductors. More particularly, sincethere is a potential difference between the sensor and the finger, whichwe denote V, and the finger touch itself induces a capacitance C, thereis a charge transfer between the finger and conductor of magnitudeQ=C*V. The charge transfer may be inferred from the current on theconductive line.

The common ground may be the electric network ground, but the methodworks also when the system is not actually connected to earth but ratherto a common ground of several systems, such as that of a flat paneldisplay, tablet PC, etc. These systems have sufficient capacity to allowthe detector to oscillate in reference to the common ground.

It should be noted that in some embodiments the system constantlyoscillates in reference to the common ground but in a preferredembodiment it only oscillates over a portion of the time, namely onlywhen signals are actually being received and processed by the detector.In other words, if there are no incoming signals to be digitized, thenthe system saves energy by not operating the oscillator.

Reference is now made to FIG. 5, which is a circuit diagram of animplementation of the embodiment of the present invention described inFIG. 4. Parts that are the same as in FIG. 4 are given the samereference numerals and are referred to only as necessary forunderstanding the theory of the operation of the embodiment. In FIG. 5,oscillator 64 is connected between ground 62 and detector 60. Theoscillator 64 oscillates the detector 60 and the detector front end,which includes two sensor conductors 70 and 72. The two conductors areconnected to the two differential inputs respectively of differentialamplifier 74. As explained above, all oscillations are in reference tothe common ground 62. The touch by the user's finger of a sensorconductor, say 70 creates capacitance 76. As there is a potentialbetween conductor 70 and the user, current passes from conductor 70through the finger to ground. Impedance 78 indicates the impedance ofthe finger. Consequently a potential difference is created betweenconductors 70 and 72. Preferably, the separation between the twoconductors 70 and 72 which are connected to the same differentialamplifier 74 is greater than the width of a finger so that the necessarypotential difference can be formed. The differential amplifier 74amplifies the potential difference, and the detector 60 processes theamplified signal and thereby determines the location of the user'sfinger. It should be noted that in alternative embodiments the sensormay be connected to a standard amplifier rather than to a differentialamplifier.

It is noted that were the oscillator not used and a d.c. currentproduced, no measurable potential difference would be produced by thetouch of the finger since the touch of the finger induces a capacitance,and thus has no effect on d.c. current.

In one embodiment of the present invention, as described above, theentire detector is oscillated in reference to the common ground. Adisadvantage of this option is that any communication between thedetector and the outside word, such as serial communication to the hostcomputer, must be adapted to compensate for the potential differencebetween the detector and the outside world and cannot use a commonground. There are numerous ways of communicating between components thathave to be isolated from each other, and one example for a way toprovide isolated communication is by using an optical link. The opticallink transforms the electrical signal into light and than back into anelectrical signal, and the level of isolation is very high. However theneed for isolation can also be overcome by applying the oscillation toonly a portion of the detector.

Reference is now made to FIG. 6, which is a theoretical circuit diagramillustrating a detector to which oscillation is only partly provided.Parts that are the same as in previous figures are given the samereference numerals and are not referred to again except as necessary forunderstanding the present embodiment. Detector 80 is the same asdetector 60 except that it is divided into two units: 82 and 84.Oscillator 86 is located between the two units 82 and 84 within thedetector 80.

The oscillation states of the components of the detector are as follows:

1) Unit 82 of detector 80 does not oscillate in reference to the commonground 62.

2) Unit 84 of the detector oscillates in reference to the common ground.Unit 84 includes the front end of the detector. It may also include anyother components of the detector.

Sensor device 88 also oscillates in reference to the common ground, byvirtue of its being connected to the detector front end, which is partof unit 84. In the present figure, the sensor device refers to thetransparent film carrying the matrix of sensors.

Using the embodiment of FIG. 6, which entails dividing the detector intotwo units, is an option available to the skilled person to be selectedin any given circumstances with regard to efficiency, convenience andcosts.

When a user's finger touches the sensor conductors within sensor device88, a capacitance 76 is created, as described above. The sensor detectssignals induced by the user's finger on the different sensor conductors.The detector 80, which includes detector units 82 and 84, processes thesensed signal and determines the location of the user's finger.

In the present embodiment, the steady portion 82 of the detector 80conducts communication to the external world without the need for anykind of isolation.

An additional advantage of the present embodiment is that usingoscillations increases power consumption. Partial application ofoscillation therefore leads to lower overall power consumption withinthe system.

A requirement of the present embodiment is to provide communicationbetween the two units of the detector since, as explained above, oneoscillates in reference to the other. The problem can be solved in anumber of ways, for example using the following alternatives:

1. Using differential signals, so that data is output on two parallellines, one a signal and one a reference. Both the signal and itsreference oscillate but the data is in fact carried in the differencebetween the two. The embodiment is described in greater detailhereinbelow with reference to FIG. 10 b, under the heading ‘floating thesystem’.

2. Using electrically isolated communication within the detector, suchas opto-isolators

3. Limiting the communication to time slots in which the front-endsection does not oscillate in reference to the other part of the system,or is at a stage in the oscillation when the two are in equilibrium.

Reference is now made to FIG. 7, which is a simplified circuit theorydiagram illustrating a preferred embodiment of the present invention. Inthe embodiment of FIG. 7, oscillations are applied to the sensor,specifically to the conductors in the sensor, and not to the detector.

In FIG. 7, an oscillator 90 provides an oscillating signal withreference to ground 92. The oscillating signal is provided as areference signal Vref to the sensor, and specifically to individualconductors in the sensor, which is to say that Vref 94 is provided toeach conductor individually.

In the figure, two sensor lines 96 and 98 are shown connected to thedifferential inputs of a single differential amplifier 100. Capacitors102 and 104 are connected between the respective sensor line and thecorresponding differential input. Finger 106 is then applied to one ofthe conductors.

In the embodiment of FIG. 7, the reference signal Vref 94 is applied toeach conductor at the output end, that is at the connections to thedifferential amplifier 100, and more specifically on the amplifier sideof the isolation capacitors 102, 104. Thus excitation and sampling areperformed at the same end of the conductor, which is the input to thedifferential amplifier.

In use an oscillation is applied to the sensor conductors by oscillatingthe reference voltage Vref 94 supplied to the sensor.

The oscillator 90 oscillates Vref 94 with respect to common ground 92.Conductors 96 and 98 therefore also oscillate with regard to the networkground. Capacitors 102 and 104 filter irrelevant low frequencies fromconductors 96 and 98 respectively. As long as the user does not touchthe sensor the signals received by both inputs of the differentialamplifier are similar and therefore no output is generated. When theuser's finger 106 touches conductor 98, a capacitance is created betweenthe user's finger 106 and conductor 98 just as before. Both theamplitude and phase of the signal propagating through the touchedconductor is altered due to the added capacitance. The potentialdifference between conductor 98 and conductor 96 is amplified by thedifferential amplifier 100 and then processed by the detector in orderto determine the location of the user's finger.

Reference is now made to FIG. 8, which is a simplified diagramillustrating a variation of the embodiment of FIG. 7. Parts that are thesame as in FIG. 7 are given the same reference numerals and are notreferred to again except as necessary for understanding the presentembodiment. The embodiment of FIG. 8 differs from FIG. 7 in that tworeference signals are used, an oscillation reference signal Va isapplied to the conductors on the ends extending into the sensor oppositeto where detection is carried out, that is away from the inputs to thedifferential amplifier. A DC reference signal is applied to the outputside of the conductors and is used to create a high reference level forthe conductive lines. Other embodiments may not include a separate DCreference signal Vref, and rely on Va alone. Vref as used in the presentembodiment, creates a high reference level for the conductors. That isto say, since the input resistance to the amplifier is very high theconductors are susceptive to noise from the environment. Connecting theconductors to a higher reference level eliminates, or at least reduces,their tendency to pick up noise. In the embodiment of FIG. 7, the Vrefsignal is used both for oscillating the conductive lines and setting theDC level. In the embodiment of FIG. 8 it is both clarified that theoscillations can be applied opposite to the detecting end of theconductor and that the oscillation and DC reference signals can beseparated. It is further noted that it is possible to apply Va—withoutuse of a separate Vref signal.

In use, an oscillation is applied to the sensor conductors byoscillating the reference voltage Va 110 supplied to the sensor.

The oscillator 90 oscillates Va 110 with respect to common ground 92.Conductors 96 and 98 therefore also oscillate with regard to the networkground. Capacitors 102 and 104 filter irrelevant low frequencies fromconductors 96 and 98 respectively. As long as the user does not touchthe sensor the signals received by both inputs of the differentialamplifier are similar and therefore no output is generated. When theuser's finger 106 touches conductor 98, a capacitance is created betweenthe user's finger 106 and conductor 98 just as before. Both theamplitude and phase of the signal propagating through the touchedconductor are altered due to the added capacitance. The potentialdifference between conductor 98 and conductor 96 is amplified by thedifferential amplifier 100 and then processed by the detector in orderto determine the location of the user's finger.

Floating the System

In order to enable oscillations of the system or part thereof, inreference to the common ground, the system or part thereof preferablyhas a certain level of isolation from the ground. The better the levelof isolation, the lower is the power lost due to the oscillations.

Reference is now made to FIG. 9, which is a simplified diagramillustrating an arrangement for floating the detection system of thepresent embodiments using an isolated DC-DC converter. In FIG. 9,Detector 120 is connected to ground 122 via isolated DC-DC converter124. Oscillator 126 provides a reference voltage to isolated detector120 so that it oscillates.

The DC-to-DC floating method may be modified so that only a portion ofthe detector oscillates in reference to the ground. Two suchmodifications are illustrated in FIGS. 10A and 10B respectively.Referring first to FIG. 10 a, the detector 130 comprises two units 132and 134. Due to the isolated DC-to-DC component 136 the detectorcomponent 134 floats in reference to the ground and the oscillator 138oscillates detector unit 134 in reference to the common ground 140.

A communication problem between the two detector units 132 and 134arises, since one of the detector units 134 oscillates whereas the otherdetector unit 136 does not.

Reference is now made to FIG. 10 b, which illustrates a possiblesolution to overcome the above-described communication problem. Partsthat are the same as in FIG. 10A are given the same reference numeralsand are not referred to again except as necessary for an understandingthe present embodiment. Detector unit 134 floats in reference to theground and oscillates, due to oscillator 136. The output signals ofdetector unit 134 oscillate in relatively the same phase as oscillator136. Output signal 142 from detection unit 134 and the oscillator output144 are inserted to a differential amplifier 146. The potentialdifference between signals 142 and 144 is amplified by the differentialamplifier 146. The output signal of differential amplifier 146 is asteady signal representation of signal 142. Thus, detecting units 132and 134 can communicate through differential amplifier 146, which servesas a communication device or channel.

Reference is now made to FIG. 11, which is an embodiment utilizing coilsfor isolating the system. Generally, coils have low impedance for lowfrequencies and high impedance for high frequencies. A power supply isprovided to the isolated portion using low frequencies, such as close toDC, but the coils manage to isolate higher frequencies such as thoseused for oscillating the detector. In FIG. 11, detector 150 is isolatedfrom its power supply, and common ground 152, using two coils 154 and156. Oscillator 158 oscillates detector 150 in reference to the commonground.

Reference is now made to FIG. 12, in which the floating coil method isimplemented such that only a part of the detector oscillates inreference to the common ground. Detector 160 is divided into two units:162 and 164. Unit 162 is isolated from its power supply and commonground 166 using two coils 168 and 170 and the oscillator 172 oscillatesunit 162 in reference to the common ground. Reference is now made toFIG. 13 which illustrates an additional method for applying oscillationsto the system or part thereof, in reference to the common ground. In theembodiment of FIG. 13, a detector 180 is connected to a first oscillator182 and a second oscillator 184. The first oscillator is connected tothe +power supply line and the second oscillator to the earth line. Inuse, the detector unit, to which oscillations are applied, is notisolated and neither is it left floating. Rather the second oscillator184 oscillates at the low potential of the system (VSS) in reference tothe common ground 186 and the first oscillator 182 oscillates at thehigh potential of the system (VCC) in reference to the power supply DClevel. As long as the two oscillators are synchronized, both in phaseand magnitude, the detector, or a portion of the detector, oscillates inreference to the common ground.

The Oscillator

As explained hereinabove, the various preferred embodiments of thepresent invention utilize an oscillator to provide a transmissionsignal, or oscillate the detector, a part of the detector or some or allof the sensor's conductors. The following section explains severaloptions for the implementation of such an oscillator.

One preferred embodiment utilizes a stand-alone oscillator. Such astand-alone oscillator is capable of oscillating either at a singlefrequency, or at a varying frequency, which, in the latter case, isdetermined by a DSP component of a digital unit associated with thedigitizer system.

An additional embodiment utilizes the DSP itself for creating theoscillations. One advantage of this option is that the phase of theoscillations can be easily synchronized for sampling. In this case DSPdigital values are provided to a D2A (Digital to Analog) component, orany equivalent arrangement, and then the analog values are filtered andamplified as required. An additional version of such an implementationmay utilize for the production of oscillations the same components thatare being used for the excitation of the stylus. For further details onthe excitation of the stylus see FIG. 9 in U.S. provisional patentapplication 60/406,662, and the corresponding description, entitled“Stylus. The figure and corresponding description are herebyincorporated herein by reference.

The same components can be used for both stylus excitation and fingersampling for the following reasons:

-   -   The finger is detected only during dedicated sampling periods,        and    -   No excitation is performed during the dedicated sampling        periods.

Reference is now made to FIG. 14, which is a simplified diagram thatdemonstrates the above-described use of the stylus excitation componentsin order to implement the oscillator. DSP 190 produces a digital signal.D/A converter 192 converts the signal to an analog representation.Amplifier 194, connected downstream of the D/A converter, amplifies theanalog signal and a switch 196 sends the signal either to an exactioncoil 98 for exciting the stylus, or to an oscillation output 200 forproviding an oscillation signal as required for the respectiveembodiment. It should be noted that the switch can be located prior tothe amplifier if different levels of amplification/output impedance arerequired for the two tasks.

The Irrelevant “Steady Noises” Problem, and its Solution

The Display Panel Irrelevant “Steady Noises” Problem

Reference is now made to FIG. 15, which is a simplified diagram whichdemonstrates what may be referred to as the display panel signalproblem. Two sensor conductors 210 and 212 oscillate in reference toground 214 by virtue of any of the above embodiments. As mentionedabove, the sensor is located over an electronic display. Capacitances216 and 218 are created between conductors 210 and 212 and the displaypanel 220. As the display panel, represented electrically by resistances220, does not oscillate in reference to the common ground 214 twosignals, (Sa) and (Sb), which may be regarded as oscillating leakagecurrents, are provided on conductors 210 and 212 respectively.

As long as the oscillation phase and magnitude do not change (Sa) and(Sb) remain identical over time. Sa and Sb are thus referred to hereinas steady noises. It is noted that the parasitic capacitance between thesensor and the display can also change due to environmental conditionsetc. This may affect the signal as well.

In an ideal environment, (Sa)=(Sb), and therefore no signaldifferentiation is amplified, by differential amplifier 222 which isconnected between the two sensors 210 and 212, unless a user's fingertouches a conductor. However, in practice, there are slight differencesin distance, overlapping area, screen structure, intermediate material,temperature, etc. (Sa)≠(Sb), and therefore, a “steady noise”: (Sa)−(Sb)is produced. The steady noise is amplified by the differential amplifier222. Such “steady noises” based on (Sa) and (Sb) exist on any two sensorconductors connected by a differential amplifier, and thus it may besaid that similar differentials to (Sa)-(Sb) are being amplified by anyof the differential amplifiers connecting sensor conductors in thesystem. The result is various amplified steady noises that, althoughsteady over time, are detected by the detector. The presence of thesesteady noises reduces the level of accuracy possible in detecting theuser's finger's location.

The Mapping Solution

Reference is now made to FIG. 16, which has an upper part 16A whichshows the display panel as a grid 230 of sensor lines 232, each pair ofsensor lines being connected to a differential amplifier 234. In onepreferred embodiment of the present invention, the solution to theproblem described above comprises mapping the various panel displayamplified signal differentiations. As demonstrated in FIG. 16B, a valueof steady noise is determined and mapped for each pair of sensorconductors. Such mapping is preferably achieved as follows:

(Sa) is the “steady noise” created on the sensor conductor connected tothe positive side of the amplifier by the flat panel display. (Sb) isthe “steady noise” created on a second conductor connected to thenegative side of the amplifier by the flat panel display. A diffamplifier connects these two conductors. The differentiation between(Sa) and (Sb) is amplified by the diff amplifier.

1. The amplified signal is converted by A/D to a digital representation

2. The DSP performs FFT/DFT on the digital signal

3. Actions 1-3 are repeated for a predetermined number of times (forexample 20 times). Averaging is then performed. Averaging minimizesvariable noises that may provide temporary distortions of themeasurement. The average value is then stored in the differential map.

4. Actions 1-4 are performed for each pair of conductors connected by adiff amplifier.

The result is a map, referred to herein as a differential map, andrepresented by FIG. 16B which includes both the magnitude and the phaseof the differential signals recorded for each sensor pair. Each recordedmagnitude phase pair represents the display panel “steady noise” of eachpair of sensor conductors connected by a differential amplifier. Themagnitude and phase are for a specific oscillation frequency.

In a preferred embodiment, the system uses a single frequency fordetection of fingers. However, in additional embodiments, more than onefrequency could be used and the system may switch between thefrequencies or even oscillate at more than one frequency simultaneously.If more than one frequency is being used, than more than one map iscreated. Preferably one map is created for each frequency.

Once the differential map is stored in memory, it can be used tocompensate for the display panel signal steady noise phenomenon.Reference is now made to FIG. 17 which is a simplified schematic diagramillustrating a two-conductor sensor arrangement exhibiting the steadynoise phenomenon. The display panel creates “steady noises” (Sa) and(Sb) on sensor conductors 240 and 242 respectively. The user's fingercreates an (Sf) signal, which is the signal it is desired to measure.The overall differential, as determined by differential amplifier 244,between the sums of signals on both sensor conductors is:{(Sa)+(Sf)}−(Sb)} The overall differential is amplified by the diffamplifier 244 and sampled by the detector 246. The DSP component 248reads the differentiation {(Sa)-(Sb)} stored within the differential map250. The DSP 250 subtracts the differential from the sampled signal. As{(Sa)+(Sf)}−(Sb)}−{(Sa−Sb)}=(Sf) the DSP is able to isolate and identifythe finger signal, and identify the finger's location.

Such a mapping process is used in the preferred embodiment of thepresent invention in order to solve the problem of steady noisesinjected by the panel display. The same method can be used in the sameand other embodiments of the present invention in order to solve anytype of steady noise problem. Examples of potential sources for steadynoise include: differences in input impedance, differences in inputcapacitance, insufficient common mode rejection, etc.

Detection of Signaling Objects Through the Mapping Process Problem andits Solutions

The mapping process creates the following problem:

An object, usually a finger, a hand or combination of fingers and hands,placed on the display panel during the mapping process creates a signal.When the hand is removed a difference over the values initially storedwithin the differential map is created. Such a difference may bemistaken by the DSP 248 for a relevant signal such as a finger signal.

For simplicity of explanation the opposite case is taken: a user'sfinger may be placed on the display panel during the actual mappingprocess. The finger inputs a signal (Hs) to a sensor conductor 242 asbefore. The sensor conductor also receives a steady noise signal (D1s)from the display panel. Another sensor conductor 240 receives a steadynoise signal (D2s) from the display panel. These two sensor conductorsare connected to the same diff amplifier 244. The differential receivedand amplified by the diff amplifier equals {(D1s)+(F1s)}−(D2s). Sometime after the mapping process is over, the finger is removed. The newdifferential amplified is now equal to: (D1s)−(D2s). The DSP subtractsthe value stored in the differential map from the new value. The resultequals: {(D1s)−(D2s)}−[{(D1s)+(F1s)}−(D2s)]=−(F1s). Realistically, the(F1s) value represent the magnitude, and the (−) sign represents thephase. This result is exactly the differentiation expected when a fingeris placed on the second sensor conductor and assuming that a finger hadnot been placed on the first sensor conductor during the mappingprocess. The DSP responds as if a finger was detected, although nofinger is actually placed on the display panel.

One embodiment of the present invention utilizes the embodimentdescribed above where the mapping process is performed once during themanufacturing process. As the expected signaling objects creating thedetection of signaling objects through the mapping process problemexplained above are mostly a user's finger, fingers, palm, fist etc; andas the manufacturing environment is one where no user is present, theproblem is solved.

The disadvantage of the above approach is the reliability of a singlemapping process. Due to system's mobility, temperature changes,mechanical changes, etc, the differentiation between the signalsproduced by the display panel on any two sensor conductors connected bya differential amplifier may change over time, rendering previouslyrecorded differential map values obsolete. A strictly controlledmanufacturing process may solve the disadvantage by ensuring that nosuch changes occur, but such a process increases costs. On the otherhand it is reasonable to believe that extreme changes in environmentalconditions will not occur during a single operation cycle of the system(i.e. from turning on the computer until shutting it down). Hence,initializing the mapping process upon system initialization shouldsuffice in most cases.

One embodiment of the present invention comprises performing mappingduring each system initialization. During the initialization the usermay be warned, either by a caption on the display panel or in any othermanner, not to touch the display panel. As the expected signalingobjects are typically the user's finger, fingers, palm, fist etc, thiswarning solves the problem. In a variation, not only is mapping carriedout at each initialization but again at every time there is a doubtregarding the validity of the differential map. Methods designated toidentify such doubts are described hereinbelow.

Methods of Identifying Doubts in the Validity of the Differential Map

In one preferred embodiment of the present invention, simultaneousidentification of more than a single finger's pattern is utilized inorder to identify a doubt in the validity of the differential map.

Thus, whenever the DSP simultaneously detects more then a singlefinger's signal pattern, a doubt in the validity of the differential mapis inferred, and the DSP launches a new mapping process.

Reference is now made to FIG. 18 with which an example of such aprocedure is described. Two groups of three lines are shown, a firstgroup labeled Fs and a second group labeled PFs. Each line representstwo sensor conductors connected to the same differential amplifier. Thelines represent sensor conductor axial signal detection, preferablyafter subtracting the steady noise from whatever source, such as thedisplay panel steady noise, as explained above. The height of each linerepresents the signal's magnitude. (Fs) and (PFs) are finger signalpatterns. If the user places a finger on the display panel during themapping process, then a finger signal pattern (PFs) is detected onlyonce the finger is removed, as explained above. Once the user actuallyplaces a finger, another finger signal pattern (Fs) is detected. Oncetwo finger signal patters are detected on the same axis a doubt in thevalidity of the differential map occurs, and the DSP launches a newmapping sequence.

It is noted that the same method can be used to identify not only morethen one finger but also one single object that is larger than a finger,such as a fist or a palm. The detection of such an object's signalpattern immediately raises doubts regarding the validity of thedifferential map.

-   -   One disadvantage of the above described method of reinitializing        in the face of a doubt is that it may enter an endless cycle of        reinitializing. Thus, in the example explained in FIG. 18, the        new mapping process is launched, but the finger that created        signal pattern (Fs) in the first place is still in place on the        display panel, damaging the validity of any reinitializing        carried out at this point.    -   An additional disadvantage is that such a system may be used        solely in systems capable of single finger detection. Once a        system is designed to detect more than a single touch, then        multiple touch is a totally legitimate input signal and cannot        be taken as an indication that reinitializing is required.

In another preferred embodiment of the present invention the detectoridentifies doubts in the validity of the differential map by utilizingthe signal's phase information. As explained above, the phase of asignal caused by a “pseudo” finger is opposite (180 degree) to the phaseof a signal caused by a real finger placed in the same position.Therefore, in a preferred embodiment, the system identifies doubts bydetecting contradictions between phase and position. However, since adifferential amplifier has two inputs, negative and positive, a realfinger located on the other input of the amplifier can lead to anopposite phase as well. Therefore, in order to avoid ambiguity, thesystem detects the position of the finger without using phaseinformation.

Such a method is described in U.S. provisional patent application60/406,662, in which the amplifier input (negative or positive) isdetermined using the magnitude of signals received by the neighborconductors.

The method is further explained as follows: If the user places a fingeron the display panel during the mapping process, and then removes it, afinger signal pattern is detected as explained above. This methoddifferentiates such a signal pattern from an actual finger that isplaced on the display panel in the following manner: Sometime after themapping process, a given differential amplifier amplifies a differentialin the signals of the two conductors it connects. This differentiation'spattern fits the magnitude of a finger's pattern.

The pattern is the result of the following scenarios:

-   -   1. A user's finger has been placed on the display panel through        the mapping process. The finger has sent a signal through the        sensor conductor connected to the positive input of the        differential amplifier, and, as a result, a signal (F1s) is sent        to the differential amplifier (N). The sensor conductor also        receives a steady noise signal (D1s) from the display panel. The        sensor conductor connected to the negative input of the        differential amplifier receives a steady noise signal (D2s) from        the display panel. The differential consequently received and        amplified by the differential amplifier equals        {(D1s)+(F1s)}−(D2s). The finger is now removed. The differential        signal amplified upon removal of the finger now equals        {(D1s)−(D2s)}. The DSP now subtracts the value stored in the        differential map from the new value. The result equals        {(D1s)−(D2s)}−[{(D1s)+(F1s)}−(D2s)]=−(F1s). Realistically, the        (F1s) value represent the magnitude, and the (−) sign represents        the phase shift.    -   2. The pattern (magnitude and phase) is the result of a real        finger currently sending a signal through the sensor conductor        connected to the negative input of the differential amplifier.

By using the magnitude of signals received and the neighboringconductors method disclosed in subchapter 4.6 of U.S. provisional patentapplication 60/406,662, which subchapter is hereby incorporated byreference, the DSP detects whether the source is the negative input ofthe differential amplifier or the positive input thereof.

-   -   If the signal's source was the sensor conductor connected to the        positive input of the differential amplifier then scenario        number 1 appears to be the case and the differential map is not        valid. A new mapping process or initialization is launched.    -   If the signal's source was the sensor conductor connected to the        negative input of the differential amplifier then scenario        number 1 mentioned above did not happen and the mapping is        valid. The DSP consequently detects a finger.

This method functions in an identical manner when the two options are:

1. A finger was sending a signal through the sensor conductor connectedto the negative input of the differential amplifier, and has now beenremoved.

2. A finger is currently sending a signal through the sensor conductorconnected to the positive input of the differential amplifier.

In order to increase the reliability of the detection of doubts in themapping, either while using phase information or while using any othermethod, the system may limit the initialization of re-learning steadynoises only to cases in which such doubts are presented for at least apredetermined minimum duration of time. Since the signals created by apseudo finger are steady and never change over time, stability over timeis an additional differentiation factor between real and pseudo signals.

In one preferred embodiment of the present invention the signal inducedby the finger is much larger then the steady noise signals. This ensuresthat a finger presence is always distinguished from the steady noise,hence enabling correct mapping process. For example, returning to FIG.15, when capacitors 216 and 218 are of lower capacitances then thefinger induced capacitance—a signal created by a finger touch is greaterthen the differential signal originating from capacitors 216 and 218.Hence, the steady noise originating from the coupling of the sensorarray and the display screen cannot be mistaken for a finger touch. Anydetected signals are translated into finger touch only when the receivedsignal is considerably higher then the steady noise. Under theseconditions, it is quite simple to identify a situation in which nofingers are present on the sensor plane to create a correct differentialmap.

One possibility for creating such conditions is ensuring an air gapbetween the conductive lines of the sensor and the display screen. Theexistence of an air gap in such a location reduces the couplingcapacitance between the sensor lines and the display screen to such alevel that finger signals are much greater then the steady noise.Another possibility comprises placing the sensor plane in closeproximity to the user finger, thus ensuring that the finger inducedsignal is greater then the steady noise.

Reference is now made to FIG. 19, which is a simplified flow chartsummarizing the three principle embodiments of the present invention. InFIG. 19, a stage 1 involves providing an oscillating electrical signal.In one embodiment the oscillating signal is transmitted, so as to bepicked up by the finger etc doing the touching. In a second embodimentthe oscillating signal is provided to one of the two groups ofconductors. The oscillating signal is capacitively connected to thesecond group of conductors in the presence of a finger touch but nototherwise. In the third embodiment the detection device or theconductors are floated with the oscillating signal and the finger touchprovides an AC short to earth.

In stage S2, the capacitive effect is detected by monitoring of theconductors in the grid. Depending on the embodiment, the capacitiveeffect may be the signal from the finger, the signal connected from theother set of conductors, or the drop in voltage due to the AC shortprovided by the finger connection. In other embodiments, any othercapacitive effect may be used.

In stage S3 the signal is filtered. Depending on the embodiment thefiltering stage may take on different forms, some of which are discussedin detail above. In stage S4 the filtered signal is used to identifywhere on the grid a touch has occurred.

It is expected that during the life of this patent many relevant imagingdevices and systems will be developed and the scope of the terms herein,particularly of the terms “stylus” and “transparent conductivematerial”, is intended to include all such new technologies a priori.

Additional objects, advantages, and novel features of the presentinvention will become apparent to one ordinarily skilled in the art uponexamination of the following examples, which are not intended to belimiting. Additionally, each of the various embodiments and aspects ofthe present invention as delineated hereinabove and as claimed in theclaims section below finds experimental support in the followingexamples.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims. All publications, patents and patentapplications mentioned in this specification are herein incorporated intheir entirety by reference into the specification, to the same extentas if each individual publication, patent or patent application wasspecifically and individually indicated to be incorporated herein byreference. In addition, citation or identification of any reference inthis application shall not be construed as an admission that suchreference is available as prior art to the present invention.

1. A detector for providing position detection of objects over a sensor,the sensor including a first and second set of conductor lines forming agrid with a plurality of junctions there between at which the conductorlines do not contact, the detector comprising: a signal generatorproviding a signal to at least one conductor line of the first set ofconductor lines; and circuitry detecting output arising from one or bothof an electromagnetic stylus and one or more fingers when present,wherein the output arising from each of the one or more fingers isdetected from at least one conductor line of the second set of conductorlines in response to the signal provided to the at least one conductorline of the first set of conductor lines, and wherein the circuitrydetects positions of one or both the electromagnetic stylus and each ofthe one or more fingers when present responsive to the output detected.2. The detector of claim 1, wherein the circuitry is operable to detectpositions of each of the electromagnetic stylus and the one or morefingers, all interacting with the sensor at the same time.
 3. Thedetector of claim 1, wherein the output arising from the electromagneticstylus and the one or more fingers is detected from same conductorlines.
 4. The detector of claim 1, wherein the circuitry is operable todetect output from transparent conductor lines.
 5. The detector of claim1, wherein the circuitry is operable to detect output from conductorlines formed from indium tin oxide (ITO), wherein the conductor linesare the first and second set of conductor lines forming the grid.
 6. Thedetector of claim 1, wherein position detection of the one or morefingers is capacitive based detection.
 7. The detector of claim 1,wherein the circuitry is operable to detect position of theelectromagnetic stylus and positions of the one or more fingersindependently.
 8. The detector of claim 1, wherein the circuitry isoperable to detect position of the electromagnetic stylus and positionsof the one or more fingers at different times.
 9. The detector of claim1, wherein the circuitry is operable to also detect output from thefirst set of conductor lines.
 10. The detector of claim 9, wherein thecircuitry is operable to detect output from first and second set ofconductor lines simultaneously.
 11. The detector of claim 1, wherein thecircuitry is operable to detect simultaneous inputs from theelectromagnetic stylus and the one or more fingers.
 12. The detector ofclaim 1, wherein the circuitry is operable to switch from applying thesignal to the first set of conductor lines and detecting output on thefirst set of conductor lines.
 13. The detector of claim 1, wherein thecircuitry is operable to apply the signal to each one of a plurality ofconductor lines in the first set of conductor lines, one line at a time.14. The detector of claim 13, wherein the circuitry is operable todetect output in the second set of conductor lines, in response to eachsignal applied to the plurality of conductor lines in the first set ofconductor lines.
 15. The detector of claim 14, wherein the circuitry isoperable to detect output in the second set of conductor lines,indicative of capacitive coupling change induced by the one or morefingers over junctions formed between a conductor line of the first setof conductor lines and conductor lines of the second set of conductorlines.
 16. The detector of claim 1, wherein the signal generatorincludes an oscillator.
 17. The detector of claim 16, wherein theoscillator is configured to oscillate with respect to a referencevoltage level, thereby to permit a capacitive current flow between eachof the one or more fingers and at least one conductor line from thefirst and second set of conductor lines.
 18. The detector of claim 1,wherein the signal generated is an AC signal.
 19. The detector of claim1, wherein the signal generator is operable to generate a signal forexciting circuitry in the electromagnetic stylus.
 20. The detector ofclaim 19, wherein the signal for exciting circuitry in theelectromagnetic stylus is applied to at least one conductor line of thefirst or second set of conductor lines.
 21. The detector of claim 1,wherein the electromagnetic stylus is internally powered using abattery.
 22. The detector of claim 1, wherein the circuitry identifieswhen a tip of the electromagnetic stylus contacts the sensor responsiveto the output arising from the electromagnetic stylus in at least oneconductor line.
 23. The detector of claim 22, wherein the circuitrydetects a frequency of energy emitted by the electromagnetic stylus andidentifies contact of the tip on the sensor responsive to detecting adefined change in the frequency of energy emitted by the electromagneticstylus.
 24. The detector of claim 1, wherein the circuitry is operativeto distinguish between positions of multiple electromagnetic stylusespresent over the sensor at the same time.
 25. The detector of claim 1,wherein the circuitry is operable to detect an oscillating signaltransferred via the junctions to conductor lines in the second set ofconductor lines, the transference being indicative of capacitivecoupling change induced by positioning of the one or more fingers overthe sensor at the respective junctions.
 26. The detector of claim 1,further comprising a tabulation of leakage signal values caused bycapacitance values for each junction.
 27. The detector of claim 1,further comprising a tabulation of signal values detected at eachjunction while both the electromagnetic stylus and the one or morefingers are removed from the sensor.
 28. The detector of claim 26,wherein the circuitry is operable to use the leakage signal values tocorrect readings at each conductor.
 29. The detector of claim 28,wherein the circuitry is operable to update the tabulation upon startupof the detector.
 30. The detector of claim 28, wherein the circuitry isoperable to update the tabulation during operation of the detector. 31.The detector of claim 1, wherein the circuitry is operable to useinterpolation to increase accuracy of the position detection.
 32. Thedetector of claim 1, wherein the circuitry is operable to determine anamount of parasitic current transfer for each junction and subtract theamount from the outputs detected.
 33. A method for providing positiondetection of objects over a sensor, the sensor including a first andsecond set of conductor lines forming a grid with a plurality ofjunctions there between at which the conductor lines do not contact, themethod comprising: providing a signal to at least one line conductorline of the first set of conductor lines; detecting output arising fromone or both of an electromagnetic stylus and one or more fingers whenpresent, wherein the output arising from each of the one or more fingersis detected from at least one conductor line of the second set ofconductor lines in response to the signal provided to the at least oneconductor line of the first set of conductor lines; and detectingpositions of one or both the electromagnetic stylus and each of the oneor more fingers responsive to the output detected.
 34. The method ofclaim 33, comprising detecting positions of each of the electromagneticstylus and the one or more fingers, all interacting with the sensor atthe same time.
 35. The method of claim 33, wherein the output arisingfrom the electromagnetic stylus and the one or more fingers is detectedfrom same conductor lines.
 36. The method of claim 33, wherein positiondetection of the one or more fingers is capacitive based detection. 37.The method of claim 33, wherein position of the electromagnetic andpositions of the one or more fingers is detected independently.
 38. Themethod of claim 33, wherein position of the electromagnetic stylus andpositions of the one or more fingers is detected at different times. 39.The method of claim 33, comprising detecting output also from the firstset of conductor lines.
 40. The method of claim 39, comprising detectingoutput from first and second set of conductor lines simultaneously. 41.The method of claim 33, comprising detecting simultaneous inputs fromthe electromagnetic stylus or the one or more fingers.
 42. The method ofclaim 33, comprising switching from applying the signal to the first setof conductor lines and detecting output on the first set of conductorlines.
 43. The method of claim 33, comprising applying the signal toeach one of a plurality of conductor lines in the first set of conductorlines, one line at a time.
 44. The method of claim 43, comprisingdetecting output in the second set of conductor lines, in response toeach signal applied to the plurality of conductor lines in the first setof conductor lines.
 45. The method of claim 44, detecting output in thesecond set of conductor lines indicative of capacitive coupling changeinduced by the one or more fingers over junctions formed between aconductor line of the first set of conductor lines and conductor linesof the second set of conductor lines.
 46. The method of claim 33,wherein the signal provided is an oscillating signal.
 47. The method ofclaim 46, wherein the signal is configured to oscillate with respect toa reference voltage level, thereby to permit a capacitive current flowbetween each of the one or more fingers and at least one conductor linefrom the first and second set of conductor lines.
 48. The method ofclaim 33, wherein the signal provided is an AC signal.
 49. The method ofclaim 33, comprising providing a signal for exciting circuitry in theelectromagnetic stylus.
 50. The method of claim 49, wherein the signalfor exciting circuitry in the electromagnetic stylus is applied to atleast one conductor line of the first or second set of conductor lines.51. The method of claim 33, wherein the electromagnetic stylus isinternally powered using a battery.
 52. The method of claim 33,comprising identifying when a tip of the electromagnetic stylus contactsthe sensor responsive to the output arising from the electromagneticstylus in at least one conductor line.
 53. The method of claim 52,comprising detecting a frequency of energy emitted by theelectromagnetic stylus and identifying contact of the tip on the sensorresponsive to detecting a defined change in the frequency of energyemitted by the electromagnetic stylus.
 54. The method of claim 33,comprising distinguishing between positions of multiple electromagneticstyluses.
 55. The method of claim 33, comprising detecting anoscillating signal transferred via the junctions to conductor lines inthe second set of conductor lines, the transference being indicative ofcapacitive coupling change induced by positioning of the one or morefingers over the sensor at the respective junctions.
 56. The method ofclaim 33, comprising determining a tabulation of signal values detectedat each junction while both the electromagnetic stylus and the one ormore fingers are removed from the sensor.
 57. The method of claim 33,comprising determining a tabulation of leakage signals values caused bycapacitance values for each junction.
 58. The method of claim 57,comprising correcting readings at each conductor responsive to theleakage signals tabulated.
 59. The method of claim 58, comprisingupdating the tabulation upon startup of the position detection of theobjects over the sensor.
 60. The method of claim 58, wherein updatingthe tabulation during operation of the position detection of the objectsover the sensor.
 61. The method of claim 33, comprising performinginterpolation to increase accuracy of the position detection.
 62. Themethod of claim 33, comprising determining an amount of parasiticcurrent transfer for each junction and subtracting the amount from theoutputs detected.